PWHT Mutiple Times on Chrome P11 and P22 2

[akvtech]

The vendor is fabricating P11 and P22 piping. Spools are placed in an oven for PWHT so the whole part. Afterwards they installed weld-in type thermowells so a second local PWHT was done. Now I find the welds on the thermowells in this B-31.3 piping were installed as a fillet welds and not full pen. They are going to cut these out and reweld and for the 3rd time PWHT these spools.
I'm concerned about the metallurgy being worked so many times.
These are DMW's as the thermowells are 316ss and the pipe 1.25cr and 2.25cr. Any thoughts on the issues this reworking might create? Thanks

 

[SnTMan]

I'd want to know that the low Cr materials retained their spec properties after the total treatment. Lab tests are needed.

Thanks,

Mike

 

[akvtech]

Are you refering to Replications on the actual parts or some other metalurgical testing?

 

[SnTMan]

akventech, it is generally done on test specimens from the same heat as the components of interest. Normally specified at time of order. As these are destructive tests they can't generally be performed on actual components, but could be done on drops if any.

Regards,

Mike

 

[metengr]

The issue with the Cr-Mo alloy steels is PWHT time at temperature versus the number of actual PWHT cycles, and the “slight” affects on notch toughness and tensile strength behavior properties. In other words, the aggregate PWHT time (longer time) will have some affect on the notch toughness behavior and ambient temperature strength properties. There should be little affect on creep strength.

If you are concerned regarding notch toughness and strength properties at ambient service temperature because of a specific application, you can have a welded coupon run to simulate the aggregate PWHT time at temperature and compare with one PWHT application, and evaluate the base metal heat affected zone (hardness and notch toughness). This is easy enough to do and would address your concerns.

 

[akvtech]

Appreciate the response Mike. These spools are installed and not likely going to be disected for destructive testing. That being said...if the historical evidence of this situation indicate failure of "Some Kind" is likely, then replacement of all the spools affected may be in order. Due to those costs I want to convince myself first that its necessary.

Regards

Alan

 

[akvtech]

Thanks Metengr.
I just want to be sure footed and not create a worse problem by over working the metal.
BTW We are at a crossroads with these thermowells and need to decide to either continue with the weld-in type or switch to flanged type we have had some cracks in the welds in the Hydrogen service (some after welding and some a month after placed in service)

 

[blacksmith37]

For heavy wall ( 6" +) Cr:Mo the intermediate PWHT would be done at lower temps to keep from dropping creep and tensile(as I remember) properties. The final PWHT (after most NDE, etc.) was the only one done at code temperature. You can imagine the heating, holding , and cooling times get very serious in a 12" thick vessel.

 

[metengr]

akventech:
Based on your recent response, I do not see an issue with using socket welded thermowelds. I would recommend using Inconel filler metal only if you are welding a dissimilar material (stainless steel thermoweld to the pipe).

 

[akvtech]

To clarify; by weld-in I meant they are cutting a hole in the pipe and welding SS thermowells straight into the P11 & P22 pipe.

 

[metengr]

Use Inconel filler metal in this case. The subsequent PWHT will not effect the performance of the pipe material. The PWHT will be governed by nominal thickness of the weld deposit.